Plating method and plating apparatus

ABSTRACT

A plating method includes holding a substrate with a substrate holder while bringing a sealing member into pressure contact with a peripheral portion of the substrate to form an enclosed internal space in the substrate holder; performing a first-stage leakage test of the substrate holder by producing a vacuum in the internal space and checking whether pressure in the internal space reaches a predetermined vacuum pressure within a certain period of time; and if the substrate holder has passed the first-stage leakage test, performing a second-stage leakage test of the substrate holder by closing off the internal space after producing the vacuum therein and checking whether a change in the pressure in the internal space reaches a predetermined value within a certain period of time.

CROSS REFERENCE TO RELATED APPLICATION

This document is a Continuation Application of U.S. application Ser. No.15/437,157 filed on Feb. 20, 2017, which is a Divisional application ofSer. No. 15/096,972, filed on Apr. 12, 2016 (Issued as U.S. Pat. No.9,611,563 granted on Apr. 4, 2017), which is a Divisional Application ofU.S. application Ser. No. 13/849,178, filed on Mar. 22, 2013 (Issued asU.S. Pat. No. 9,340,891, granted on May 17, 2016), which claims priorityto Japanese Patent Application No. 2012-071546, filed Mar. 27, 2012, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a plating method and a platingapparatus for plating a surface of a substrate, and more particularly toa plating method and a plating apparatus for forming a plating film infine interconnect trenches, holes, or resist openings provided on asurface of a substrate, such as a semiconductor wafer, or for formingbumps (extruding electrodes), to be electrically connected to electrodesof a package, on a surface of a semiconductor wafer. A plating methodand a plating apparatus according to the present invention can also beused for filling via holes with metal in manufacturing of an interposeror spacer, having a large number of via plugs penetrating through it,which is to be used in three-dimensional packaging of semiconductorchips.

Description of the Related Art

It is a common practice in TAB (tape automated bonding) or flip chip toform protruding connection electrodes (bumps) of gold, copper, solder ornickel, or of multiple layers of such metals at predetermined portions(electrodes) of a surface of a semiconductor chip, having interconnectsformed therein, so that the semiconductor chip can be electricallycoupled via the bumps to electrodes of a package or TAB electrodes.There are various methods usable for formation of bumps, such aselectroplating, vapor deposition, printing, and ball bumping. Inparticular, electroplating, which can form fine bumps and can beperformed in a relatively stable manner, is widely used as the number ofI/O in a semiconductor chip increases and the electrode pitch becomessmaller.

The electroplating method can be classified roughly into a jet method orcup method in which a substrate, such as a semiconductor wafer, is heldin a horizontal position with a surface to be plated facing downward,and a plating solution is jetted upward onto the surface to be plated,and a dip method in which a substrate is held in a vertical position ina plating bath and a plating solution is injected upward into theplating bath while the plating solution overflows the plating bathduring plating. Electroplating using the dip method has advantages of asmall footprint and good release of bubbles which could adversely affecta quality of plating, and is therefore considered suitable for bumpplating in which plating is performed on relatively large-sized holesand which requires a considerably long plating time.

A conventional electroplating apparatus using the dip method has asubstrate holder for detachably holding a substrate, such as asemiconductor wafer, with its front surface (to-be-plated surface)exposed and a peripheral portion of the surface sealed. Theelectroplating apparatus is configured to perform plating of the surfaceof the substrate by immersing the substrate, together with the substrateholder, in a plating solution. The electroplating apparatus has theadvantage of good release of bubbles.

Since the substrate holder is kept immersed in the plating solutionduring plating, the peripheral portion of the substrate, held by thesubstrate holder, must be securely sealed so that the plating solutionwill not intrude into a back surface (a surface opposite to the surfaceto be plated) and a peripheral area of the substrate where electricalcontacts are in contact with the substrate. For example, the substrateholder has a pair of support members (holding members) designed todetachably hold the substrate therebetween and is provided with sealingmembers in one of the support members. One of the sealing members isbrought into pressure contact with the other support member to seal agap between the support members. The other sealing member is broughtinto pressure contact with the peripheral portion of the substrate,which is placed and held on the other support member, to seal a gapbetween the substrate and the support member.

In order to prevent leakage of a processing liquid (e.g., a platingsolution) in such substrate holder, there has been proposed severalapproaches including: optimization of a shape and a fixing manner of thesealing member; regular cleaning of the sealing member (e.g., afterevery processing); regular replacement of the sealing member;improvement of accuracy of pre-processing (formation of a seed layer ora resist film) of a substrate; minimization of a positional error onsetting of the substrate in the substrate holder; and regularreadjustment of the sealing member.

However, it is fairly difficult to achieve completely sealed statebecause of deterioration of the sealing member or other causes.Especially when performing plating of a substrate surface to fill finerecesses, such as trenches or via holes, with a plating film, a platingsolution having good permeability is typically used so that the platingsolution can easily and securely enter the fine recesses. Use of such aplating solution makes it more difficult to establish the completelysealed state. It is also generally difficult to detect leakage of theplating solution into the substrate holder. Once the leakage of theplating solution occurs, the plating solution will intrude into thesubstrate holder and adhere to the peripheral portion and the backsurface of the substrate. The plating solution attached to the substratemay be transferred to a substrate transport device and may contaminatethe plating apparatus in its entirety. In addition, the leaked platingsolution may corrode electrical contacts, resulting in poor feeding ofelectric current.

The applicant has proposed a substrate holder having at least one pairof electrical conductors, which are to be short-circuited by a leakedplating solution, in order to detect (through passage of electriccurrent between the electrical conductors) leakage of a plating solutionupon actual plating of a substrate held by the substrate holder, carriedout by immersing the substrate, together with the substrate holder, inthe plating solution (see Japanese Patent Laid-Open Publication No.2004-52059). The applicant has also proposed a substrate holder which isconfigured to supply a pressurized gas into a space formed between asubstrate, held by the substrate holder, and the substrate holder andsurrounded by a sealing member, and to detect leakage of the gas fromthe sealing member by detecting a decrease in the pressure of the gas(see Japanese Patent Laid-Open Publication No. 2003-277995).

A pre-plating test of leakage of a plating solution has been proposed.In particular, after sealing a peripheral portion of a substrate with asealing member, the possibility of leakage of a plating solution into aspace defined by the sealing member is checked e.g. by depressurizing orpressurizing a hermetic space formed by the sealing member (see JapanesePatent Laid-Open Publication No. 2002-531702).

A pre-plating test of the integrity of sealing has been proposed. Inparticular, when a substrate holder holds a substrate while sealing aperipheral portion of the substrate with a sealing member, an internalspace in the substrate holder, defined by the substrate, isdepressurized e.g. by applying a small vacuum of about −0.05 atm to arecess in which the substrate is housed. The internal space is thenclosed off. If a change in the vacuum is within a predetermined level,e.g. 10%, within a certain time period, e.g. 5 seconds, then theintegrity of sealing is determined to be verified (the leakage test ispassed) (see Japanese Patent Laid-Open Publication No. 2007-509241).

It is generally difficult to determine the sealed state of the sealingmember merely by measuring the pressure in the internal space in thesubstrate holder after evacuating or pressurizing the internal space.Moreover, when a trace amount of plating solution has leaked, a volumeratio of a volume of the internal space to the amount of the leakedplating solution is considerably high and, inversely, a change in thepressure in the internal space is considerably small. For example, whenthe volume of the internal space is 500 cc and the amount of leakedplating solution is 0.05 cc, the change in the pressure in the internalspace is 1/10000. Therefore, even a high-precision pressure sensor couldfail to detect the sealed state. In particular, the leakage of theplating solution with even a trace amount is required to be securelydetected either before or after plating in order to continuously andstably operate the plating apparatus.

The leakage of the plating solution in the substrate holder can causecorrosion of the electrical contacts of the substrate holder, anincrease in the electrical contact resistance, and the like. Therefore,in a case of conducting a post-plating leakage test of the platingsolution, a maintenance work, including cleaning of the substrate holderand replacement of parts, may be required depending on the degree of theleakage of the plating solution.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above situation. Itis therefore an object of the present invention to provide a platingmethod and a plating apparatus which can quickly and securely detectserious failure of a sealed state of a sealing member and can securelydetect leakage of even a trace amount of plating solution prior toplating of a substrate.

In order to achieve the object, the present invention provides a platingmethod including: holding a substrate with a substrate holder whilebringing a sealing member into pressure contact with a peripheralportion of the substrate to form an enclosed internal space in thesubstrate holder; performing a first-stage leakage test of the substrateholder by producing a vacuum in the internal space and checking whetherpressure in the internal space reaches a predetermined vacuum pressurewithin a certain period of time; and if the substrate holder has passedthe first-stage leakage test, performing a second-stage leakage test ofthe substrate holder by closing off the internal space after producingthe vacuum therein and checking whether a change in the pressure in theinternal space reaches a predetermined value within a certain period oftime.

According to the plating method, leakage of a plating solution e.g., dueto an apparent operational error or inadequate maintenance can bedetected early and quickly by carrying out the first-stage leakage testwhich can be performed in a relatively short time. Further, thefirst-stage leakage test can reduce the burden on the second-stageleakage test. The second-stage leakage test can securely and quicklydetect serious trouble with the sealing of the sealing member of thesubstrate holder, making it possible to take appropriate action on thesealing trouble.

In a preferred embodiment of the present invention, checking whether thechange in the pressure in the internal space reaches the predeterminedvalue within the certain period of time comprises: producing a vacuum ina leak-free master container; closing off the master container in whichthe vacuum is produced; measuring pressure difference between pressurein the internal space and pressure in the master container; and checkingwhether the pressure difference becomes equal to or larger than apredetermined value within a certain period of time.

The change in the pressure in the internal space is thus detected bymeasuring the difference between the pressure in the internal space andthe pressure in the master container. This makes it possible to moreaccurately detect a very small change in the pressure in the internalspace as compared to the case where the change in the pressure in theinternal space is directly detected by using a pressure sensor.

In a preferred embodiment of the present invention, if the substrateholder has passed the second-stage leakage test, a third-stage leakagetest is performed by forming a hermetic space between the substrate heldby the substrate holder and a seal case arranged so as to cover thesubstrate; supplying a tracer gas into the hermetic space; evacuatingair from the internal space; and checking whether the air evacuated fromthe internal space contains the tracer gas.

The third-stage leakage test, which may require a relatively long timeand is optionally carried out for the substrate holder that has passedthe second-stage leakage test, can securely detect leakage of a traceamount of plating solution which can occur in the sealing member.

In a preferred embodiment of the present invention, holding thesubstrate with the substrate holder comprises holding a substrate with asubstrate holder while bringing a substrate-side sealing member intopressure contact with a peripheral portion of the substrate and bringinga holder-side sealing member into pressure contact with a surface of thesubstrate holder to form an enclosed internal space in the substrateholder, the hermetic space is divided into a substrate-side hermeticspace around the substrate-side sealing member and a holder-sidehermetic space around the holder-side sealing member, and thethird-stage leakage test is performed on at least one of thesubstrate-side hermetic space and the holder-side hermetic space.

This embodiment makes it possible to detect whether one or both of thesubstrate-side sealing member and the holder-side sealing member willcause leakage of a plating solution, and to take appropriate action onthe relevant sealing member(s). It takes a long time to carry out thethird-stage leakage test individually for the holder-side hermetic spaceand for the substrate-side hermetic space. Therefore, when there is noneed to detect which one of the holder-side sealing member and thesubstrate-side sealing member will cause leakage of a plating solution,the third-stage leakage test may be carried out for the single hermeticspace, without dividing it into the two hermetic spaces, in order toshorten the test time.

The present invention also provides another plating method platingmethod including: holding a substrate with a substrate holder whilebringing a sealing member into pressure contact with a peripheralportion of the substrate to form an enclosed internal space in thesubstrate holder; and performing a leakage test by forming a hermeticspace between the substrate held by the substrate holder and a seal casearranged so as to cover the substrate, supplying a tracer gas into thehermetic space, evacuating air from the internal space, and checkingwhether the air evacuated from the internal space contains the tracergas.

The leakage test may be performed periodically, or as an off-line testperformed before the start or after the end of operation of theapparatus. When performing the off-line leakage test, a dummy substratemay be used instead of the substrate.

In a preferred embodiment of the present invention, the leakage test isperformed in a substrate loading unit for loading and unloading thesubstrate into and from the substrate holder. Thus, the leakage test ofthe substrate holder can be performed immediately after the substrate isheld by the substrate holder and immediately before the start of aplating process.

The present invention also provides a plating apparatus including: asubstrate holder having a sealing member which is brought into pressurecontact with a peripheral portion of the substrate to form an enclosedinternal space in the substrate holder when holding the substrate, thesubstrate holder having an internal passage communicating with theinternal space; a suction coupling coupled to a suction line extendingfrom a vacuum source and detachably mounted to the substrate holder soas to communicate with the internal passage; a pressure sensor forchecking whether pressure in the internal space reaches a predeterminedvacuum pressure within a certain period of time when producing a vacuumin the internal space through the suction line; and a pressure changedetection section for detecting a change in the pressure in the internalspace after the vacuum is produced in the internal space and then theinternal space is closed off In a preferred embodiment of the presentinvention, the pressure change detection section includes: a mastercontainer which is assured that any leakage does not occur and iscoupled to the vacuum source, and a differential pressure sensor formeasuring a differential pressure between the pressure in the mastercontainer and the pressure in the internal space.

In a preferred embodiment of the present invention, the platingapparatus further includes: a seal case arranged so as to cover asurface of the substrate held by the substrate holder to form a hermeticspace between the seal case and the substrate holder, the substratebeing housed in the hermetic space; a tracer gas introduction device forintroducing a tracer gas into the hermetic space; and a tracer gastester for detecting whether the tracer gas is contained in a gasflowing through the suction line.

In a preferred embodiment of the present invention, the sealing memberis a substrate-side sealing member; the substrate holder has thesubstrate-side sealing member and a holder-side sealing member which arebrought into pressure contact with the peripheral portion of thesubstrate and a surface of the substrate holder, respectively, to formthe enclosed internal space in the substrate holder when holding thesubstrate; the seal case has a partition sealing member for dividing thehermetic space into a substrate-side hermetic space around thesubstrate-side sealing member and a holder-side hermetic space aroundthe holder-side sealing member.

According to the present invention, the leakage of the plating solutionin the substrate holder due to an apparent operational error orinadequate maintenance or the like can be detected early and quickly bythe first-stage leakage test which can be performed in a relativelyshort time. The second-stage leakage test, which is performed on thesubstrate holder that has passed the first-stage leakage test, cansecurely and quickly detect serious trouble with the sealed state of thesealing member of the substrate holder, making it possible to takeappropriate action on the sealing trouble. The leakage test according tothe present invention thus makes it possible to infer the cause ofleakage and early detect trouble with the sealing member, therebyreducing a time required for maintenance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall layout plan view of a plating apparatus accordingto an embodiment of the present invention;

FIG. 2 is a schematic perspective view of a substrate holder;

FIG. 3 is a plan view of the substrate holder shown in FIG. 2;

FIG. 4 is a right side view of the substrate holder shown in FIG. 2;

FIG. 5 is an enlarged view of a portion A of FIG. 4;

FIG. 6 is a diagram illustrating a first-stage leakage test and asecond-stage leakage test for the substrate holder holding a substrate;

FIG. 7 is a diagram illustrating a third-stage leakage test for thesubstrate holder holding the substrate;

FIG. 8 is a flow chart showing an exemplary process flow of thefirst-stage leakage test and the second-stage leakage test; and

FIG. 9 is a diagram schematically showing a main part of the platingapparatus according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the drawings.

FIG. 1 shows an overall layout plan view of a plating apparatusaccording to an embodiment of the present invention. As shown in FIG. 1,the plating apparatus includes two cassette tables 12 each receivesthereon a cassette 10 in which substrates W, such as semiconductorwafers, are housed, an aligner 14 for aligning an orientation flat or anotch of the substrate in a predetermined direction, and a spin rinsedrier 16 for drying the substrate after plating by rotating it at a highspeed. Near these units is provided a substrate loading unit 20 on whichthe substrate holder 18 is placed. This substrate loading unit 20 isconfigured to load the substrate into the substrate holder 18 and unloadthe substrate from the substrate holder 18. Further, in the center ofthese units is disposed a substrate transport device 22 which is atransport robot for transporting the substrate between these units.

The plating apparatus further includes a stock unit 24 for storing (andtemporarily storing) substrate holders 18 therein, a pre-wetting bath 26for immersing the substrate in pure water, a pre-soaking bath 28 foretching away an oxide film formed on a surface of a film (e.g., a seedlayer) of the substrate, a first water-cleaning bath 30 a for cleaningthe surface of the pre-soaked substrate, a blow bath 32 for draining thesubstrate after cleaning, a plating bath 34 for plating the substrate,and a second water-cleaning bath 30 b for cleaning the plated substrate.The stock unit 24, the pre-wetting bath 26, the pre-soaking bath 28, thefirst water-cleaning bath 30 a, the blow bath 32, the secondwater-cleaning bath 30 b, and the plating bath 34 are arranged in thisorder from the substrate loading unit side. The plating bath 34 includesan overflow bath 36 and a plurality of plating cells 38 housed in theoverflow bath 36. Each plating cell 38 is configured to receive onesubstrate therein and perform plating, e.g., copper plating, on thesurface of the substrate.

The plating apparatus further includes a substrate holder transportdevice 40, driven e.g., by a linear motor for transporting the substrateholder 18, together with the substrate, between the above-describedbathes and units. This substrate holder transport device 40 is arrangedbeside these bathes and units. The substrate holder transport device 40has a first transporter 42 for transporting the substrate between thesubstrate loading unit 20 and the stock unit 24, and a secondtransporter 44 for transporting the substrate between the stock unit 24,the pre-wetting bath 26, the pre-soaking bath 28, the water-cleaningbath 30 a, the second water-cleaning bath 30 b, the blow bath 32, andthe plating bath 34. The substrate holder transport device 40 mayinclude only the first transporter 42 without being provided with thesecond transporter 44.

Paddle drive devices 46 are provided each for driving a paddle (notshown) disposed in each plating cell 38 as an agitator for agitating aplating solution. The paddle drive devices 46 are located next to theoverflow bath 36 at the opposite side of the substrate holder transportdevice 40.

The substrate loading unit 20 includes a flat stage plate 52 which islaterally slidable along rails 50. Two substrate holders 18, parallel toeach other, are placed horizontally on the stage plate 52. After onesubstrate is transferred between one substrate holder 18 and thesubstrate transport device 22, the stage plate 52 is slid laterally andthe other substrate is transferred between the other substrate holder 18and the substrate transport device 22.

As shown in FIGS. 2 through 5, the substrate holder 18 includes a firstholding member (base holding member) 54 having a rectangular plate shapeand made of e.g., vinyl chloride, and a second holding member (movableholding member) 58 rotatably coupled to the first holding member 54through a hinge 56 which allows the second holding member 58 to open andclose with respect to the first holding member 54. Although in thisembodiment the second holding member 58 is configured to be openable andclosable through the hinge 56, it is also possible to dispose the secondholding member 58 opposite to the first holding member 54 and to movethe second holding member 58 away from and toward the first holdingmember 54 to thereby open and close the second holding member 58.

The second holding member 58 includes a base portion 60 and aring-shaped seal holder 62. The seal holder 62 is made of vinyl chlorideso as to enable a retaining ring 64, which will be described later, toslide well. An inwardly-projecting substrate-side sealing member 66 isfixed to an upper surface of the seal holder 62. The substrate-sidesealing member 66 is placed in pressure contact with a peripheralportion of the surface of the substrate W to seal a gap between thesubstrate W and the second holding member 58 when the substrate W isheld by the substrate holder 18. A holder-side sealing member 68 isfixed to a surface, facing the first holding member 54, of the sealholder 62. This holder-side sealing member 68 is placed in pressurecontact with the first holding member 54 to seal a gap between the firstholding member 54 and the second holding member 58 when the substrate Wis held by the substrate holder 18. The holder-side sealing member 68 islocated outwardly of the substrate-side sealing member 66.

As shown in FIG. 5, the substrate-side sealing member 66 is sandwichedbetween the seal holder 62 and a first mounting ring 70 a which issecured to the seal holder 62 by fastening tools 69 a, such as bolts.The holder-side sealing member 68 is sandwiched between the seal holder62 and a second mounting ring 70 b which is secured to the seal holder62 by fastening tools 69 b, such as bolts.

The seal holder 62 of the second holding member 58 has a stepped portionat a periphery thereof, and the retaining ring 64 is rotatably mountedto the stepped portion via a spacer 65. The retaining ring 64 isinescapably held by an outwardly projecting retaining plates 72 (seeFIG. 3) mounted to a side surface of the seal holder 62. This retainingring 64 is made of a material having high rigidity and excellent acidcorrosion resistance, for example titanium, and the spacer 65 is made ofa material having a low friction coefficient, for example PTEF, so thatthe retaining ring 64 can rotate smoothly.

Inverted L-shaped clampers 74, each having an inwardly projectingportion and located outside of the retaining ring 64, are provided onthe first holding member 54 at equal intervals along a circumferentialdirection of the retaining ring 64. Outwardly projecting portions 64 bare provided on the retaining ring 64 along the circumferentialdirection of the retaining ring 64 at positions corresponding topositions of the clampers 74. A lower surface of the inwardly projectingportion of each clamper 74 and an upper surface of each projectingportion 64 b of the retaining ring 64 are tapered in opposite directionsalong the rotational direction of the retaining ring 64. A plurality(e.g., three) of upwardly protruding dots 64 a are provided on theretaining ring 64 in predetermined positions along the circumferentialdirection of the retaining ring 64. The retaining ring 64 can be rotatedby pushing and moving each dot 64 a from a lateral direction by means ofa rotating pin (not shown).

When the second holding member 58 is open, the substrate W is insertedinto the central portion of the first holding member 54, and the secondholding member 58 is then closed through the hinge 56. Subsequently theretaining ring 64 is rotated clockwise so that each projecting portion64 b of the retaining ring 64 slides into the inwardly projectingportion of each clamper 74. As a result, the first holding member 54 andthe second holding member 58 are fastened to each other and locked byengagement between the tapered surfaces of the projecting portions 64 bof the retaining ring 64 and the tapered surfaces of the clampers 74.The lock can be released by rotating the retaining ring 64counterclockwise to disengage the projecting portions 64 b of theretaining ring 64 from the inwardly projecting portions of the clampers74. When the second holding member 58 is locked in the above-describedmanner, the lower end of the inner downwardly-protruding portion of thesubstrate-side sealing member 66 is placed in pressure contact with theperipheral portion of the surface of the substrate W held by thesubstrate holder 18, while the lower end of the outerdownwardly-protruding portion of the holder-side sealing member 68 isplaced in pressure contact with the surface of the first holding member54, whereby the sealing members 66 and 68 are uniformly pressed to sealthe gap between the substrate W and the second holding member 58 and thegap between the first holding member 54 and the second holding member58, respectively.

When the substrate W is held by the substrate holder 18, a holder-sideinternal space R₁ is formed in the substrate holder 18 as shown in FIG.5. An inner circumferential side of the holder-side internal space R₁ issealed by the substrate-side sealing member 66, and an outercircumferential side of the holder-side internal space R₁ is sealed bythe holder-side sealing member 68. This holder-side internal space R₁communicates with a substrate-side internal space R₂ which is formedbetween the substrate holder 18 and the substrate W, so that a hermeticinternal space R is formed by the holder-side internal space R₁ and thesubstrate-side internal space R₂ which are in communication with eachother.

The first holding member 54 has a protruding portion 82 in a ring shapecorresponding to a size of the substrate W. The protruding portion 82has a support surface 80 which contacts the peripheral portion of thesubstrate W to support the substrate W. The protruding portion 82 hasrecesses 84 arranged at predetermined positions along a circumferentialdirection of the protruding portion 82.

As shown in FIG. 3, a plurality of electrical conductors (electricalcontacts) 86 (e.g., 12 conductors as illustrated), coupled respectivelyto wires extending from external contacts provided on a hand 90, aredisposed in the recesses 84 of the protruding portion 82. When thesubstrate W is placed on the support surface 80 of the first holdingmember 54, ends of the electrical conductors 86 are exposed in a springystate on the surface of the first holding member 54 at positions besidethe substrate W to contact lower portions of the electrical contacts 88shown in FIG. 5.

The electrical contacts 88, to be electrically coupled to the electricalconductors 86, are secured to the seal holder 62 of the second holdingmember 58 by fastening tools 89, such as bolts. The electrical contacts88 each have a leaf spring-like contact portion lying outside thesubstrate-side sealing member 66 and projecting inwardly. This contactportion is springy and bends easily. When the substrate W is held by thefirst holding member 54 and the second holding member 58, the contactportions of the electrical contacts 88 make elastic contact with theperipheral surface of the substrate W supported on the support surface80 of the first holding member 54.

The second holding member 58 is opened and closed by a not-shownpneumatic cylinder and by the weight of the second holding member 58itself. More specifically, a through-hole 54 a is formed in the firstholding member 54, and the pneumatic cylinder is provided so as to facethe through-hole 54 a when the substrate holder 18 is placed on thesubstrate loading unit 20. The second holding member 58 is opened byextending a piston rod of the pneumatic cylinder to lift up a pressingrod (not shown) through the through-hole 54 a to thereby push up theseal holder 62 of the second holding member 58. The second holdingmember 58 is closed by its own weight when the piston rod is retracted.

A pair of approximately T-shaped hands 90 is coupled to the ends of thefirst holding member 54 of the substrate holder 18. These hands 90 serveas a support when the substrate holder 18 is transported and when thesubstrate holder 18 is held in a suspended state. In the stock unit 24,outwardly projecting portions of the hands 90 are placed on an uppersurface of a peripheral wall of the stock unit 24, whereby the substrateholder 18 is suspended in a vertical position. When transporting thesubstrate holder 18 from the stock unit 24, the hands 90 of thesuspended substrate holder 18 are gripped by the transporter 42 or 44 ofthe substrate holder transport device 40. Also in the pre-wetting bath26, the pre-soaking bath 28, the water-cleaning bath 30 a, the secondwater-cleaning bath 30 b, the blow bath 32, and the plating bath 34, thesubstrate holder 18 is held in a suspended state with the hands 90placed on top of peripheral wall of the bath.

As schematically shown in FIG. 6, an internal passage 100 is formed inthe first holding member 54 so as to communicate with the internal spaceR through the substrate-side internal space R₂, which is formed betweenthe substrate holder 18 and the substrate W when the substrate W is heldby the substrate holder 18. The internal space R is formed between thesubstrate holder 18 and the substrate W and sealed (hermeticallyenclosed) by the sealing members 66 and 68. As shown in FIGS. 2 and 3,the internal passage 100 is coupled to a suction port 102 provided inthe hand 90.

As schematically shown in FIG. 6, the substrate loading unit 20 isprovided with a suction coupling 106 having a seal ring 104. Thissuction coupling 106 is coupled to the suction port 102 of the hand 90through the seal ring 104 which establishes a hermetically sealed state.The suction coupling 106 is coupled via a coupling plate 110 to anactuator 108, such as an air cylinder, which is disposed in apredetermined position on the substrate loading unit 20. When performinga leakage test of the substrate holder 18 holding the substrate W, theactuator 108 is driven to connect the suction coupling 106 to thesuction port 102 of the hand 90. When the leakage is not performed, thesuction coupling 106 is disconnected from the suction port 102.

The suction coupling 106 is coupled to a suction line 114 extending froma vacuum source 112, such as a vacuum pump. The suction line 114 isprovided with a main on-off valve 118 and a pressure sensor 116 formeasuring pressure in the suction line 114.

The plating apparatus further includes a master container 120 which isassured that any leakage does not occur. A differential pressure testline 122 extends from the master container 120 to the suction line 114at a junction upstream of the main on-off valve 118. The suction line114 and the differential pressure test line 122 are provided with anon-off valve 124 a and an on-off valve 124 b, respectively, which arelocated upstream of the junction where the suction line 114 and thedifferential pressure test line 122 join. A differential pressure sensor126 is provided upstream of the on-off valves 124 a and 124 b formeasuring differential pressure between pressure in the internal space Rand pressure in the master container 120 when the on-off valves 124 aand 124 b are closed. These configurations constitute a pressure changedetection section 128 which detects a change in the pressure in theinternal space R after producing a vacuum in the internal space Rthrough the suction line 114 and then closing off the internal space R.

The change in the pressure in the internal space R is detected by usingthe differential pressure sensor 126 which measures the differentialpressure between the pressure in the internal space R and the pressurein the master container 120 when the on-off valves 124 a and 124 b areclosed. This makes it possible to more accurately detect a very smallchange in the pressure in the internal space R as compared to the casewhere a change in the pressure in the internal space R is directlydetected using a pressure sensor.

There is provided a bypass line 130 which branches off from the suctionline 114 at a point upstream of the on-off valve 124 a and joins thesuction line 114 at a point between the on-off valve 124 a and the mainon-off valve 118. The bypass line 130 is provided with on-off valves 132a and 132 b and a tracer gas tester 138 located between the on-offvalves 132 a and 132 b. The tracer gas tester 138 includes a tester body136 provided with a tracer gas sensor 134. An atmospheric air measuringhose 140 having an on-off valve 139 is coupled to the tester body 136.The tracer gas sensor 134 of the tracer gas tester 138 detects whetheror not air (gas), flowing through the bypass line 130, contains a tracergas.

As shown in FIG. 7, a cylindrical seal case 142 with a closed top and anopen bottom, which is movable vertically and horizontally, is disposedon the substrate loading unit 20. An annular tracer gas sealing member146 and an annular partition sealing member 148 are mounted to a lowersurface of the seal case 142. When the seal case 142 is lowered, thetracer gas sealing member 146 is brought into pressure contact with thesurface of the first holding member 54 of the substrate holder 18 alonga sealing line 144 as indicated by two-dot chain line shown in FIG. 3 toseal (i.e., hermetically close) a gap between the seal case 142 and thefirst holding member 54. When the seal case 142 is lowered, thepartition sealing member 148 is also brought into pressure contact withthe seal holder 62 of the second holding member 58 to seal (i.e.,hermetically close) a gap between the seal case 142 and the seal holder62.

The seal case 142 is moved from a retreated position to a position justabove the substrate holder 18, and then lowered to bring the tracer gassealing member 146 and the partition sealing member 148 into pressurecontact with the surface of the first holding member 54 and the surfaceof the seal holder 62 of the second holding member 58, respectively,thereby forming two hermetic spaces S₁ and S₂ between the substrateholder 18 and the seal case 142. The space S₁ is a holder-side hermeticspace that houses therein the holder-side sealing member 68 for sealingthe gap between the first holding member 54 and the second holdingmember 58, and the space S₂ is a substrate-side hermetic space thathouses therein the substrate-side sealing member 66 which is pressedagainst the peripheral portion of the substrate W to seal the gapbetween the substrate W and the second holding member 58.

The plating apparatus of this embodiment further includes tracer gasintroduction devices 150 a and 150 b for introducing a tracer gas intothe holder-side hermetic space S₁ and the substrate-side hermetic spaceS₂, respectively. The tracer gas introduction device 150 a forintroducing the tracer gas into the holder-side hermetic space S₁ has agas supply line 158 a connecting a tracer gas tank 156 a to a gascoupling 154 a mounted to a gas supply port 152 a, which is formed inthe seal case 142 and communicates with the holder-side hermetic spaceS₁. The gas supply line 158 a is provided with a pressure control valve160 a and an on-off valve 162 a which are arranged in this order along agas flow direction.

An air supply line 166 a, extending from an air supply source 164 a, iscoupled to the gas supply line 158 a at a point downstream of the on-offvalve 162 a. This air supply line 166 a is provided with an on-off valve168 a. A gas exhaust line 174 a, provided with an on-off valve 172 a, iscoupled to a gas exhaust port 170 a, which communicates with theholder-side hermetic space S₁ and is formed in the seal case 142.

The tracer gas is supplied into the holder-side hermetic space S₁ byopening the on-off valve 162 a on the gas supply line 158 a and theon-off valve 172 a on the gas exhaust line 174 a. When a predeterminedamount of the tracer gas is supplied into the holder-side hermetic spaceS₁, the on-off valve 162 a and the on-off valve 172 a are both closed toseal the tracer gas in the holder-side hermetic space S₁. When theon-off valve 168 a on the air supply line 166 a and the on-off valve 172a on the gas exhaust line 174 a are opened, air is introduced into theholder-side hermetic space S₁ to purge the tracer gas from theholder-side hermetic space S₁.

The tracer gas introduction device 150 b for introducing the tracer gasinto the substrate-side hermetic space S₂ has a similar construction tothe tracer gas introduction device 150 a for introducing the tracer gasinto the holder-side hermetic space S₁. Therefore, the same referencenumerals, but using a letter “b” instead of a letter “a”, are used forthe corresponding components, and a duplicate description thereof isomitted. The gas supply port 152 b and the gas exhaust port 170 bcommunicate with the substrate-side hermetic space S₂.

In this embodiment, helium gas is used as the tracer gas. The helium gasis lighter than air and exists in air only in an amount of 5 ppm and istherefore distinguishable from other gases. G-Fine helium gas leaktester, manufactured by Cosmo Instruments Co., Ltd., is used as thetracer gas tester 138. The tester 138 of this embodiment can detect leakof 0.0006 mL/min to 1000 mL/min of the helium gas (tracer gas), and candetect leak of 0.1 cc/min in 11 seconds.

A gas mixture of 5% hydrogen and 95% nitrogen may also be used as thetracer gas. This gas mixture is dilution hydrogen (H₂+N₂) which is safe,clean, and incombustible. This gas mixture is available at a lower pricethan helium gas, stably available as a multipurpose industrial gas, andeasily diffuses. A background concentration of this gas mixture is aslow as 0.5 ppm. It is also possible to use argon gas which is heavierthan air (1.784 g/L, 1.38 times heavier than air). The argon gas iscontained in the air at a concentration of 0.93 vol %.

A sequence of plating processes performed by the above-described platingapparatus will now be described. First, one substrate is removed fromthe cassette 10 mounted on the cassette table 12 by the substratetransport device 22. The substrate is placed on the aligner 14, whichthen aligns an orientation flat or a notch of the substrate in apredetermined direction. After the alignment, the substrate istransported to the substrate loading unit 20 by the substrate transportdevice 22.

Two substrate holders 18 stored in the stock unit 24 are simultaneouslygripped by the first transporter 42 of the substrate holder transportdevice 40, and transported to the substrate loading unit 20. Thesubstrate holders 18 are lowered in a horizontal position until the twosubstrate holders 18 are simultaneously placed on the stage plate 52 ofthe substrate loading unit 20. Two pneumatic cylinders are then actuatedto open the second holding members 58 of the substrate holders 18,respectively.

In this state, the substrate is inserted into the center-side substrateholder 18 by the substrate transport device 22, and the pneumaticcylinder is reversely actuated to close the second holding member 58.The second holding member 58 is then locked by means of a locking andunlocking mechanism provided above the substrate loading unit 20. Aftercompletion of the loading of the substrate into the substrate holder 18,the stage plate 52 is slid laterally, and a substrate is then loadedinto the other substrate holder 18 in the same manner. Thereafter, thestage plate 52 is returned to its original position.

The substrate W is secured to the substrate holder 18 with its frontsurface (to-be-plated surface) exposed in an opening of the substrateholder 18. The substrate-side sealing member 66 seals the gap betweenthe peripheral portion of the substrate W and the second holding member58 and the holder-side sealing member 68 seals the gap between the firstholding member 54 and the second holding member 58 so as not to allowthe plating solution to enter the internal space R. These sealingmembers 66 and 68 enable electrical connection between the electricalcontacts 88 and a portion of the substrate W that does not contact theplating solution. The wires extending from the electrical contacts 88are connected to the external contacts provided on the hand 90 of thesubstrate holder 18. Therefore, an electric current can be fed to a film(e.g., a seed layer) of the substrate W by establishing electricalconnection between a power source and the external contacts on the hand90.

Next, a pre-plating first-stage leakage test is performed in order todetermine whether or not the gap between the peripheral portion of thesubstrate W and the second holding member 58 is sealed (i.e.,hermetically closed) by the substrate-side sealing member 66 and whetheror not the gap between the first holding member 54 and the secondholding member 58 is sealed (i.e., hermetically closed) by theholder-side sealing members 68 in a manner to prevent intrusion of theplating solution. A process flow of the first-stage leakage test isshown in FIG. 8 (steps 1 to 4). As shown in FIG. 6, the suction coupling106 is coupled to the suction port 102 of the hand 90 of the substrateholder 18, and only the main on-off valve 118 and the on-off valve 124 aof the suction line 114 are opened to evacuate the internal space R (theholder-side internal space R₁ and the substrate-side internal space R₂)(step 1). The evacuation is performed for a certain period of time(e.g., two seconds), which is measured by a timer (step 2). After thecertain period of time has elapsed, it is determined whether or not thepressure in the internal space R has reached a predetermined vacuumpressure (step 3). The pressure in the internal space R is measured bythe pressure sensor 116.

If the pressure in the internal space R has not reached thepredetermined vacuum pressure within the certain period of time, it isdetermined that leakage of the plating solution can occur (i.e., thesubstrate holder 18 has failed in the first-stage leakage test) due toan abnormality caused by an apparent operational error, inadequatemaintenance, or the like. Examples of such an abnormality are that thesubstrate W is not held by the substrate holder 18, the sealing members66 and 68 are not mounted to the substrate holder 18, the sealingmembers 66 and 68 are not mounted to the seal holder 62 properly, andthere is a serious failure of the sealing members 66 and 68. Appropriatemeasures are then taken to deal with the abnormality (step 4). Forexample, if the substrate W is not held by the substrate holder 18, itis likely that a failure has occurred in the plating apparatus. In thiscase, the plating apparatus is stopped and checked. In a case where thesubstrate W is held by the substrate holder 18, the substrate holder 18is recovered and checked.

In this manner, the first-stage leakage test can quickly and securelydetect the occurrence of leakage of the plating solution due to theapparent operational error or inadequate maintenance or the like, andcan reduce a burden on the below-described second-stage leakage test.

If the pressure in the internal space R has reached the predeterminedvacuum pressure within the certain period of time, i.e., the substrateholder 18 has passed the first-stage leakage test, a second-stageleakage test of the substrate holder 18 is performed. Process flow ofthe second-stage leakage test is also shown in FIG. 8 (steps 5 to 8).While the suction coupling 106 is coupled to the suction port 102 of thehand 90 of the substrate holder 18, only the main on-off valve 118 andthe on-off valve 124 a of the suction line 114 and the on-off valve 124b of the differential pressure test line 122 are opened to produce avacuum simultaneously in the internal space R and the master container120 so that the internal space R and the interior of the mastercontainer 120 have the same vacuum pressure therein. Thereafter, themain on-off valve 118 and the on-off valve 124 a of the suction line 114and the on-off valve 124 b of the differential pressure test line 122are closed (step 5) and left for a certain period of time (e.g., 5seconds). This period of time is measured by a timer (step 6). Duringthe certain period of time, a so-called build-up test is performed bymeasuring the difference between the pressure in the internal space Rand the pressure in the master container 120 by means of thedifferential pressure sensor 126 so as to detect whether or not thepressure difference becomes equal to or larger than a predeterminedvalue (as a result of a decrease in the degree of vacuum in the internalspace R) (step 7). The use of the build-up test method can moreaccurately detect a very small change in the pressure in the internalspace R as compared to a case where a change in the pressure in theinternal space R is directly detected by using a pressure sensor.

Although in this embodiment the change in the pressure in the internalspace R is measure by means of the pressure change detection section 128according to the differential pressure method using the differentialpressure sensor 126, it is possible to use the pressure sensor 116 as apressure change detection section, i.e., to directly measure the changein the pressure in the internal space R without separately providing thepressure change detection section 128.

If the difference between the pressure in the internal space R and thepressure in the master container 120 becomes equal to or larger than thepredetermined value, then the sealed state provided by the sealingmembers 66 and 68 is determined to be imperfect (i.e., the substrateholder 18 has failed in the second-stage leakage test). The reasons forimperfect sealing of the sealing members 66 and 68 include thefollowings.

(1) The substrate W was not held in a proper position on the substrateholder 18.

(2) There was an abnormality in a resist (which coats a substratesurface in order to mask portions not to be plated), such as thepresence of surface irregularities on the resist, the existence ofcutout portion in the resist just under the sealing member, too smalldiameter of the resist, and non-concentric resist formation with thesubstrate.

(3) There was damage to the sealing members 66 and 68, such as a scratchin the sealing surface(s) of the sealing members 66 and 68, a loss ofthe elasticity of the sealing members 66 and 68 due to the platingsolution.

(4) A resist that has peeled off a preceding substrate has adhered tothe substrate-side sealing member 66 of the substrate W.

The following measures can be taken for the substrate holder 18 that hasfailed in the second-stage leakage test (step 8).

(1) The substrate W is removed from the substrate holder 18 once, thesubstrate W is rotated (e.g., through 180 degrees) so as to change amanner of contact between the resist on the substrate surface and thesubstrate-side sealing member 66, and then the substrate W is held againby the substrate holder 18.

(2) The substrate W is removed from the substrate holder 18, and thesubstrate is replaced with the next substrate. Conditions of the resiston the substrate W that has been removed from the substrate holder 18are checked.

(3) The substrate holder 18 is replaced with a new one, and the old oneis checked. It is desirable to store a spare substrate holder(s) in theplating apparatus, or to design the plating apparatus to be capable ofcarrying in and out a substrate holder even during operation.

Subsequent to the second-stage leakage test, the substrate holder 18 canbe subjected to a third-stage leakage test.

First, as shown in FIG. 7, the seal case 142 is moved from the retreatedposition to a position just above the substrate holder 18 holding thesubstrate W, and then lowered to bring the tracer gas sealing member 146into slight contact with the first holding member 54 at a position alongthe sealing line 144 and simultaneously bring the partition sealingmember 148 into slight contact with the surface of the seal holder 62 ofthe second holding member 58, thereby forming the holder-side hermeticspace S₁ and the substrate-side hermetic space S₂ between the substrateholder 18 and the seal case 142. These hermetic spaces S₁ and S₂ arehermetically sealed (enclosed) by the tracer gas sealing member 146 andthe partition sealing member 148.

The third-stage leakage test is performed just below the locking andunlocking mechanism. Thus, when the test is not conducted, the seal case142 is in the retreated position which is located away from the positionbelow the locking and unlocking mechanism. When the test is conducted,the seal case 142 is inserted into a space between the substrate holder18 and the locking and unlocking mechanism. This movement of the sealcase 142 is performed by means of a seal case movement mechanism (notshown).

In this state, the third-stage leakage test is performed on theholder-side hermetic space S₁. Specifically, the tracer gas, such ashelium gas, is supplied into the holder-side hermetic space S₁ byopening only the on-off valve 162 a of the gas supply line 158 a of thetracer gas introduction device 150 a and the on-off valve 172 a of thegas exhaust line 174 a. When the predetermined amount of the tracer gasis supplied into the holder-side hermetic space S₁, the on-off valve 162a and the on-off valve 172 a are both closed to seal the tracer gas inthe holder-side hermetic space S₁. In this state, the suction coupling106 is coupled to the suction port 102 of the hand 90 of the substrateholder 18 in the same manner as described above, and only the on-offvalves 132 a and 132 b of the bypass line 130 and the main on-off valve118 of the suction line 114 are opened, so that the air (gas) isevacuated from the internal space R. The air (gas), evacuated from theinternal space R, is collected in the tester body 136 of the tracer gastester 138.

Whether or not the air (gas) collected in the tester body 136 containsthe tracer gas, which is helium gas in this embodiment, is then detectedby means of the tracer gas sensor 134. The helium gas is present innature only at a concentration of 5 ppm. Therefore, there is adifference in the concentration of the helium gas between the air (gas)containing the helium gas and natural air. Based on this difference inthe helium-gas concentration, it is possible to detect whether or notthe collected air (gas) contains the helium gas therein. If the air(gas) collected in the tester body 136 contains the tracer gas (heliumgas), then it is determined that the sealed state provided by theholder-side sealing member 68, which is located in the holder-sidehermetic space S₁ and mounted to the second holding member 58 of thesubstrate holder 18, is imperfect and that there is leakage between theholder-side sealing member 68 and the first holding member 54 (thesubstrate holder 18 has failed in the third-stage leakage test).

By utilizing the tracer gas leakage in this manner, even a trace amountof the leakage of the plating solution between the holder-side sealingmember 68 and the first holding member 54 can be securely detected(predicted) prior to the plating process. This holds true for thebelow-described case where even a trace amount of plating solution leaksthrough the gap between the substrate-side sealing member 66 and thesurface of the substrate W.

Next, the tracer gas (the helium gas) is supplied into and sealed in thesubstrate-side hermetic space S₂ in a manner similar to theabove-described manner of supplying the tracer gas into the holder-sidehermetic space S₁. Thereafter, air (gas) is evacuated from the internalspace R. The air (gas), evacuated from the internal space R, iscollected in the tester body 136 of the tracer gas tester 138. Whetheror not the air (gas) collected in the tester body 136 contains thetracer gas (the helium gas) is then detected by means of the tracer gassensor 134. If the air (gas) collected in the tester body 136 containsthe tracer gas (the helium gas), then it is determined that the sealedstate provided by the substrate-side sealing member 66, which is locatedin the substrate-side hermetic space S₂ and mounted to the secondholding member 58 of the substrate holder 18, is imperfect and thatthere is leakage between the substrate-side sealing member 66 and thesurface of the substrate W (the substrate holder 18 has failed in thethird-stage leakage test).

When it is determined that there is leakage between the holder-sidesealing member 68 and the first holding member 54 or between thesubstrate-side sealing member 66 and the surface of the substrate W,measures are taken for the substrate holder 18 in the same manner as theabove-described measures to be taken when the substrate holder 18 hasfailed in the second-stage leakage test. Because the third-stage leakagetest are performed individually for the holder-side hermetic space S₁and the substrate-side hermetic space S₂, it is possible to determinewhether the substrate-side sealing member 66 or the holder-side sealingmember 68 is likely to cause the leakage of the plating solution and totake appropriate measures for that sealing member.

According to this embodiment, the leakage of the plating solution due toan apparent operational error or inadequate maintenance can be detectedearly and quickly by the first-stage leakage test which can be done in arelatively short time. Moreover, the first-stage leakage test can reducethe burden on the second-stage leakage test. The second-stage leakagetest can securely and quickly detect serious sealing failure of thesealing members 66 and 68 of the substrate holder 18, making it possibleto take appropriate actions on the possible leakage of the platingsolution. The third-stage leakage test, which requires a relatively longtime and which is optionally carried out for the substrate holder 18that has passed the second-stage leakage test, can securely detectleakage of even a trace amount of plating solution.

The third-stage leakage test may not be conducted every time thesubstrate W is held by the substrate holder 18, because the state of thesubstrate or the sealing members 66 and 68 rarely changes drastically.Further, generally it takes a long time to conduct the third-stageleakage test. Accordingly, conducting the third-stage leakage testfrequently leads to a considerable decrease in the throughput. In viewof this, the third-stage leakage test, which checks the state of thesubstrate holder, may be performed separately from the first-stageleakage test and the second-stage leakage test as an off-line test whichdoes not affect the productivity. Such an off-line test may be performedperiodically or before or after the operation of the apparatus. In theoff-line leakage test (i.e., the third-stage leakage test), in order toeliminate the influence of the resist on the substrate surface so as tocheck the state of the substrate holder accurately, it is preferred touse a dummy substrate (a substrate having no resist formed thereon),i.e., to perform the leakage test on the substrate holder holding adummy substrate. Use of such a dummy substrate in the leakage test canavoid a decrease in the throughput. The dummy substrate may be suppliedto the substrate holder 18 from the cassette 10 set on the cassettetable 12 or a dummy substrate cassette provided in the apparatus.

Although in this embodiment the third-stage leakage test is performedfor both of the holder-side hermetic space S₁ and the substrate-sidehermetic space S₂, the third-stage leakage test may be performed only onone of the holder-side hermetic space S₁ and the substrate-side hermeticspace S₂. For example, based on the results of the third-stage leakagetest for the holder-side hermetic space S₁, the third-stage leakage testfor the substrate-side hermetic space S₂ may be omitted. Morespecifically, if it is determined, based on the results of thethird-stage leakage test for the holder-side hermetic space S₁, that thesealed state provided by the holder-side sealing member 68 is imperfectand that there is leakage between the holder-side sealing member 68 andthe first holding member 54 (i.e., the substrate holder 18 has failed inthe third-stage leakage test), then the third-stage leakage test for thesubstrate-side hermetic space S₂ may be omitted.

Plating is performed on a substrate held by the substrate holder 18 thathas passed the pre-plating leakage test. The substrate holder 18 thathas failed in the pre-plating leakage test is opened, and a substrate isremoved from that substrate holder 18 and returned to the cassette 10 onthe cassette table 12. The failed substrate holder 18 is gripped by thefirst transporter 42 of the substrate holder transport device 40 andreturned to the stock unit 24 as an unusable holder. The failedsubstrate holder 18 may be removed from the stock unit 24 after theoperation of the plating apparatus, and may be subjected to appropriateremedy.

According to the above-discussed embodiment, it is possible to detectwhether or not the gap between the peripheral portion of the substrate Wand the second holding member 58 is properly sealed by thesubstrate-side sealing member 66 and whether or not the gap between thefirst holding member 54 and the second holding member 58 is properlysealed by the holder-side sealing members 68. A sequence of platingprocesses, including the pre-plating leakage test for all the substrateholders 18, can be performed systematically in a successive manner.

The substrate holder 18 may have a sensor for sensing contact statebetween the substrate and the electrical contacts 88 and detectingwhether the contact state is poor or not simultaneously or before orafter the pre-plating leakage test. If the contact state is determinedto be poor, the same measures as those for the substrate holder that hasfailed in the pre-plating leakage test can be taken for the substrateholder 18 with the poor contact state.

The substrate, held by the substrate holder 18 that has passed thepre-plating leakage test, is subjected to the following plating process.

The substrate holder 18, which holds the substrate and has passed thepre-plating leakage test, is gripped by the first transporter 42 of thesubstrate holder transport device 40 and transported to the pre-wettingbath 26, where the substrate holder 18 is lowered until the substrate,together with the substrate holder 18, is immersed in a pre-wettingliquid in the pre-wetting bath 26. As described above, the substrateholder 18 that has failed in the pre-plating leakage test and has beenreturned to the stock unit 24 is not allowed to be used and is nottransported to the pre-wetting bath 26.

The substrate holder 18, which holds the substrate and has passed thepre-plating leakage test, may be transported to the stock unit 24 onceand stored temporarily in a vertically suspended state in the stock unit24, and then may be transported to the pre-wetting bath 26.

Although not shown, instead of providing the substrate loading unit 20on which two substrate holders 18 are placed horizontally, it ispossible to provide a fixing station which is configured to receive twosubstrate holders from the first transporter 42 and support the twosubstrate holders vertically (or in an inclined state with a small anglewith respect to the vertical direction). The substrate holders can bebrought into a horizontal position by rotating the fixing station,holding the substrate holders in the vertical position, by 90 degrees.

Although in this embodiment the one locking and unlocking mechanism isprovided, it is possible to provide two locking and unlocking mechanismsadjacent to each other and to simultaneously perform locking andunlocking of two substrate holders by the two locking and unlockingmechanisms.

Next, the two substrate holders 18 loaded with the substrates aretransported to the pre-soaking bath 28 in the same manner as describedabove. In the pre-soaking bath 28, an oxide film on each substrate isetched away, so that a clean metal surface is exposed. Thereafter, thesubstrate holders 18 loaded with the substrates are transported to thefirst water-cleaning bath 30 a in the same manner as described above,and the surface of each substrate is cleaned with the pure water storedin the first water-cleaning bath 30 a.

After water cleaning, the two substrate holders 18 loaded with thesubstrates are gripped by the second transporter 44 of the substrateholder transport device 40 and are transported to the plating bath 34which is filled with the plating solution. Each substrate holder 18 issuspended and held at a predetermined position in one of the platingcells 38. The second transporter 44 of the substrate holder transportdevice 40 sequentially repeats the above operations to sequentiallytransport the substrate holders 18 to the plating cells 38 of theplating bath 34 and suspend the substrate holders 18 in the platingcells 38.

After suspending the substrate holders 18 in all the plating units 38 iscompleted, plating of the surface of each substrate is performed in thefollowing manner. A plating voltage is applied between each substrate Wand an anode (not shown) in the plating cell 38, while the paddle isreciprocated parallel to the surface of the substrate by the paddledrive device 46. During plating of the substrate, the substrate holder18 is suspended from the top of the plating cell 38 through the hands90, so that electricity is fed from a plating power source to a film(e.g., a seed layer) of the substrate through the electrical conductors86 and the electrical contacts 88. The plating solution circulates fromthe overflow bath 36 to the plating cell 38 through a circulation line(not shown) basically at all times during operations of the platingapparatus. The plating solution is maintained at a constant temperatureby a constant-temperature device provided in the circulation line.

After the completion of plating, the application of the plating voltageand the reciprocation of the paddle are stopped. Thereafter, the twosubstrate holders 18 loaded with the plated substrates W aresimultaneously gripped by the second transporter 44 of the substrateholder transport device 40, and are transported to the secondwater-cleaning bath 30 b in the same manner as described above, so thatthe surface of each substrate is cleaned with the pure water stored inthe second water-cleaning bath 30 b.

After cleaning, the substrate holders 18 loaded with the substrates Ware transported to the blow bath 32, where air or N₂ gas blows towardthe substrates W held by the substrate holders 18 to remove waterdroplets therefrom to thereby dry the substrates W.

The second transporter 44 of the substrate holder transport device 40sequentially repeats the above operations to successively transfer thesubstrate holders 18, each loaded with the plated substrate, to the blowbath 32.

The substrate holders 18, each loaded with the plated substrate W afterbeing dried in the blow bath 32, are gripped by the first transporter 42of the substrate holder transport device 40 and are placed on the stageplate 52 of the substrate loading unit 20.

The second holding member 58 of the center-side substrate holder 18 isfirstly unlocked by the locking and unlocking mechanism, and thepneumatic cylinder is actuated to open the second holding member 58. Itis preferable to provide a spring element (not shown), other than theelectrical contacts 88, on the second holding member 58 so as to preventthe substrate W from sticking to the second holding member 58 when itopens. Thereafter, the plated substrate W is removed from the substrateholder 18 by the substrate transport device 22 and transported to thespin rinse drier 16, where the substrate W is cleaned with pure waterand then spin-dried (drained) by high-speed rotation of the substrate W.The dried substrate W is returned to the cassette 10 by the substratetransport device 22.

After or simultaneously with returning the substrate to the cassette 10,the stage plate 52 is slid laterally and the other substrate is removedfrom the other substrate holder 18. The substrate is thenspin-rinse-dried by the spin rinse drier 16, and the dried substrate isreturned to the cassette 10 in the same manner.

A new substrate W is loaded into the substrate holder 18 from which theplated substrate has been removed, and the new substrate W is subjectedto the sequential processes. When there is no new substrate W to beprocessed, the substrate holder 18 with no substrate is gripped by thefirst transporter 42 of the substrate holder transport device 40 andreturned to a predetermined place in the stock unit 24.

In this manner, all the substrates are removed from the substrateholders 18, spin-dried by the spin rinse drier 16, and returned to thecassette 10. The sequence of operations is completed when all thesubstrates have been plated, cleaned, and dried and all the substrateholders 18 are returned to predetermined places in the stock unit 24.

FIG. 9 is a diagram schematically showing a main part of the platingapparatus according to another embodiment of the present invention. Theplating apparatus of this embodiment differs from the above-describedplating apparatus in use of the seal case 142 not having the partitionsealing member 148 (see FIG. 7). Thus, when the tracer gas sealingmember 146 of the seal case 142 is brought into pressure contact withthe surface of the first holding member 54 of the substrate holder 18along the sealing line 144 (see FIG. 3), a hermetic space S is formedbetween the seal case 142 and the substrate holder 18. The holder-sidesealing member 68 and the substrate-side sealing member 66 are locatedin this hermetic space S. The plating apparatus of this embodiment isprovided with a single tracer gas introduction device 150 forintroducing the tracer gas into the hermetic space S.

This tracer gas introduction device 150 for introducing the tracer gasinto the hermetic space S has a similar construction to theabove-described tracer gas introduction device 150 a for introducing thetracer gas into the holder-side hermetic space S₁. Therefore, the samereference numerals, but not using the letter “a”, are used for theequivalent components, and a duplicate description thereof will beomitted. The gas supply port 152 and the gas exhaust port 170communicate with the hermetic space S.

In this embodiment, the third-stage leakage test is performed asfollows. The tracer gas sealing member 146 of the seal case 142 isbrought into slight contact with the first holding member 54 of thesubstrate holder 18 at a position along the sealing line 144 (see FIG.3), thereby forming the hermetic space S between the substrate holder 18and the seal case 142. This hermetic space S is hermetically sealed(enclosed) by the tracer gas sealing member 146. Thereafter, the tracergas (the helium gas) is supplied into and sealed in the hermetic space Sin the same manner as described above. The air (gas) is then evacuatedfrom the internal space R, and the air (gas), evacuated from theinternal space R, is collected in the tester body 136 of the tracer gastester 138. Whether or not the air (gas) collected in the tester body136 contains the tracer gas (the helium gas) is detected by the tracergas sensor 134.

If the air (gas) collected in the tester body 136 contains the tracergas (the helium gas), then it is determined that the sealed stateprovided by at least one of the substrate-side sealing member 66 and theholder-side sealing member 68, both mounted to the second holding member58 of the substrate holder 18, is imperfect and that there is leakagebetween the holder-side sealing member 68 and the first holding member54 and/or between the substrate-side sealing member 66 and the surfaceof the substrate W (the substrate holder 18 had failed in thethird-stage leakage test).

The third-stage leakage test according to this embodiment cannotdetermine which one of the substrate-side sealing member 66 and theholder-side sealing member 68 can cause the leakage of the platingsolution. However, the third-stage leakage test according to thisembodiment has the advantage that the test of the substrate holder 18can be completed in a shorter time.

While the present invention has been described with reference topreferred embodiments, it is understood that the present invention isnot limited to the embodiments described above, but is capable ofvarious changes and modifications within the scope of the inventiveconcept as expressed herein.

What is claimed is:
 1. A method of checking leakage of a substrateholder, comprising: supporting one surface of a substrate with a firstholding member of the substrate holder, which is for use in plating ofthe substrate, while placing a second holding member of the substrateholder in contact with other surface of the substrate, with the othersurface of the substrate exposed to an atmospheric pressure through anopening of the second holding member; sealing a gap between the firstholding member and the second holding member with a first protrudingportion of the second holding member, and sealing a peripheral portionof the substrate with a second protruding portion of the second holdingmember, thereby forming an internal space in the substrate holder withthe first holding member, the second holding member, and the substrate;performing a first-stage leakage test of the substrate holder byproducing a vacuum in the internal space, with the other surface of thesubstrate exposed to the atmospheric pressure, and checking whetherpressure in the internal space reaches a predetermined vacuum pressurewithin a predetermined period of time to check a sealed state providedby the first protruding portion and the second protruding portion; andperforming a second-stage leakage test of the substrate holder, whichhas passed the first-stage leakage test, by closing off the internalspace after producing the vacuum therein and checking whether a changein the pressure in the internal space reaches a predetermined valuewithin a predetermined period of time to further check the sealed stateprovided by the first protruding portion and the second protrudingportion.
 2. The method according to claim 1, wherein checking whetherthe change in the pressure in the internal space reaches thepredetermined value within the predetermined period of time comprises:producing a vacuum in a leak-free master container; closing off themaster container in which the vacuum is produced; measuring pressuredifference between the pressure in the internal space and pressure inthe master container by a differential pressure sensor; and checkingwhether the pressure difference reaches a predetermined value within acertain period of time.
 3. The method according to claim 1, furthercomprising: performing a third-stage leakage test of the substrateholder, which has passed the second-stage leakage test, by locating aseal case so as to cover the surface, which is exposed through theopening, of the substrate held by the substrate holder, sealing a gapbetween the first holding member of the substrate holder and the sealcase, thereby forming a hermetic space between the substrate holder andthe seal case, supplying a tracer gas into the hermetic space whileevacuating air from the internal space, and checking whether the airevacuated from the internal space contains the tracer gas to furthercheck the sealed state provided by the first protruding portion and thesecond protruding portion.
 4. The method according to claim 3, wherein:the hermetic space is divided into a substrate-side hermetic space and aholder-side hermetic space by sealing a gap between the second holdingmember of the substrate holder and the seal case, the second protrudingportion being located in the substrate-side hermetic space, and thefirst protruding portion being located in the holder-side hermeticspace; and the third-stage leakage test is performed on at least one ofthe substrate-side hermetic space and the holder-side hermetic space. 5.The method according to claim 1, wherein the substrate is asemiconductor wafer.